Method for inspecting and adjusting cutter blades

ABSTRACT

A cutter inspection device and a method of operating the device for determining cutter blade settings by measuring an air gap is disclosed. The device comprises an electronic measuring unit, with a capacitance probe that measures an air gap having a value dependent upon a blade setting. The air gap is formed between the capacitance probe and the cutter blade for some blade setting measurements and in other blade setting measurements, the air gap is formed between the capacitance probe and a contact element in contact with a surface or edge of a cutter blade.

United States Patent Pigage et al.

[ Feb.8,1972

[54] METHOD FOR INSPECTING AND ADJUSTING CUTTER BLADES [72] Inventors:Robert F. Pigage, Rochester; Arthur B.

Ryan, Victor; Robert E. Smith,

Rochester, all of N.Y.

[73] Assignee: The Gleason Works, Rochester, NY.

221 Filed: on. 1, 1968 [2]] App]. No.: 764,223

[52] US. Cl. ..324/61 R, 33/174 L [51 Int. Cl. ..G0ln 27/26 [58] FieldofSearch ..324/6l;33/l74, 175

[56] References Cited UNITED STATES PATENTS 3,504,279 3/1970 Foster etal. ..324/6l 2,417,062 3/1947 Coake ...33/l74 2,842,738 7/1958 Warnick..324/6l 3,428,889 2/1969 Mayer ..324/6l FOREIGN PATENTS OR APPLICATIONS591,490 8/ 1947 Great Britain ..324/61 Primary Examiner-Edward E.Kubasiewicz Attamey-Cushman, Darby & Cushman and Morton A. Polster [57]ABSTRACT A cutter inspection device and a method of operating the devicefor determining cutter blade settings by measuring an air gap isdisclosed. The device comprises an electronic measuring unit, with acapacitance probe that measures an air gap having a value dependent upona blade setting. The air gap is formed between the capacitance probe andthe cutter blade for some blade setting measurements and in other bladesetting measurements, the air gap is formed between the capacitanceprobe and a contact element in contact with a surface or edge of acutter blade.

2Claims,7DrawingFigures 4 EMf/VT PATENTEBFEB 8 I972 SHEET 2 [IF 3ATTORNED PATENTED FEB 8 I972 SHEET 3 BF 3 ZNVENTOR ATTORNEY METHOD FORINSPECTING AND ADJUSTING CUTTER BLADES BRlEF DESCRIPTION OF THEINVENTION The present invention relates to a cutter inspection andtruing operation and, in particular, to a cutter inspection apparatusand method which measures blade positions more accurately thanpreviously known inspection techniques due to the novel use of anelectronic measuring unit which measures the dimension of an air gapformed between a capacitance probe and a cutter blade or contactelement.

The present invention is part of an overall, general develop ment of theGleason Works which includes several inventions besides that disclosedand claimed herein. This development includes other inventions such as anovel structural orientation of center parts, a novel cradle housing andcradle assembly, a novel ratio control or ratio change mechanism, novelcontrol means for the generating train, a novel workhead assembly, novelmeans for conveying gears or gear blanks to the cutting stations andtransferring them between cutting stations with novel means forautomatic stock division in going from one station to the other, a novelcontrol means for controlling the operation of the work loading andunloading and automatic stock division mechanisms, a novel chamferingmeans designed to remove burrs, etc., from the roughed gears, and othernovel structures and techniques, all of which are being covered in aseries of patent applications. These applications are: Ser. Nos.764,212, 764,213, 764,214, 764,215, 764,216, 764,217, 764,218, 764,219,764,220, 764,221, 764,222, filed contemporaneously herewith, and thedisclosures of which are all incorporated herein by reference.

While the present development is primarily intended to be used fortruing cutters utilized in the production of hypoid pinions for theautomotive industry, it will be apparent to those skilled in the artthat the present invention can be used for checking and truing othertypes of gear cutters where great accuracy in the cutter blade settingsis required.

After the blades on a cutter have been sharpened, it is necessary toinspect and, if necessary, correct the blade positions on the cutterprior to remounting the cutter on the pinion generating machine. Thisoperation is performed on a cutter inspection machine.

Heretofore, the radial distances of the blade cutting edges relative tothe central axis of a cutter have been detennined by means of a probewhich contacted the cutting edge of the blade or the cutting side faceof the blade at a point behind the leading cutting edge of the blade.The first method of determining the radial setting of the blade hasproved unsatisfactory since a sharpened edge has irregularities such asnicks and burrs which can cause measurements to be off by values up to0.001 of an inch or more when an accuracy of twenty-millionths of aninch is desired.

With the second method of determining the radial distance of the cuttingedge of the blade from the axis of the cutter, a second type of errorhas been introduced into the measurements. By contacting the cuttingside faces of the blades rather than the leading cutting edge, the errorin measurements due to irregularities such as burrs and nicks along theleading edge is eliminated. However, the cutting side faces are alwaysrelieved back of their cutting edges and such a relief is usuallyaccomplished by grinding these faces as helical surfaces coaxial withthe cutter axis so that upon sharpening of a cutter by grinding back thefront faces of the blades, the relationship between the side cuttingedge, the tip cutting edge and the cutter axis will not be changed. Withthis helical surface, if the cutter is not indexed so that the probecontacts the cutting side face the same distance behind the leading edgefor each blade, the measurement made does not correlate with the radialdistance from the cutting edge to the axis of the cutter and thusresults in inaccurate values. As with the first method of determiningthe radial trueness of a cutting edge, this error has seriously affectedthe accuracy with which the blade positions can be checked.

ln cutting operations where great accuracy is required, such as in thecutting of spiral bevel and hypoid pinions for use in the automotiveindustry, the errors in measurement resulting from the above methodsrequire further truing of the cutter while it is on the piniongenerating machine thereby involving costly down time. The presentinvention improves the accuracy of radial truing to such an extent that,even with the inherent errors introduced by transferring the cuttersfrom the cutter inspection machine to the pinion generating machine, theneed for truing the cutter once it has been mounted on the piniongenerating machine is eliminated.

The electronic measuring unit and method of the present developmenteliminate the inaccuracies encountered when using the devices andmethods of the prior art by measuring the average value of a gap betweena capacitance probe and a side cutting face of the blade which isimmediately adjacent to, and which includes a part of, the cutting edgeof the blade. It has been discovered that such a measurement eliminateserrors inherent in prior methods of measurement because the capacitancetransducer measures the average gap between the end of the probe and theside cutting face (and the included cutting edge), thereby giving ahighly accurate reading (to ten-millionths of an inch) of the radialdistance between the cutting edge and the axis of the cutter. lnaddition, since there is no longer any attempt to take measurements acertain distance back from the cutting edges, the inconsistenciesresulting from the second prior art method are also eliminated.

Briefly, the cutter truing device of the present invention comprises abasic embodiment in which the cutter is mounted in a work indexer and acapacitance probe is mounted in a holder which can be positionedadjacent the blades of a cutter retained in the indexer. The measurementis carried out by rotating the indexer and thus moving the blades,relative to the probe, from the rear portion of the cutting side face tothe leading or cutting edge of the blade. The capacitance between theprobe and blade (which affects the output voltage of the measuring unit)gradually increases as the relative movement between the probe and bladecauses the distance between the probe and blade to decrease. Thecapacitance reaches a readily discemable peak at a point where thecutting edge is well within the effective area of the probe face andthen starts to decrease as the relative motion between the blade andprobe is continued. After the capacitance probe is set in apredetermined position relative to the master blade of the cutter, thedimension of the air gap between the cutting side face of the blade andthe capacitance probe is measured by the magnitude of an output voltageof the measuring unit. The output voltage is proportional to the spacingbetween the probe and the cutting side face of the blade. Themeasurement is carried out by moving the blades, relative to the probe,from the rear portion of the cutting side face to the leading or cuttingedge of the blade. The capacitance between the probe and blade (whichaffects the output voltage of the measuring unit) gradually increases asthe relative movement between the probe and the blade causes thedistance between the probe and blade to diminish, The capacitancereaches a peak as the cutting edge is reached and then starts todecrease as the sensing area of the probe starts to pass beyond thecutting edge. In this way, through the use of a properly calibrateddistance meter which is responsive to the output voltage of themeasuring unit, the radial trueness of a cutter can be determinedwithout the necessity of the probe actually coming into contact with thecutting edge of a blade and without the need for the probe to contactthe blade a certain distance behind the cutting edge thereby eliminatingthe errors inherent in the measurements made according to prior methods.

A second embodiment of the present invention is employed to measure thecutting side angle of a blade, and in this embodiment the spacingbetween the probe and a contact element which contacts the cutter bladeis measured by the magnitude of an output voltage that is directlyproportional to the spacing between the probe and the contact element.As the pivotally mounted contact element contacts the blade, the gapbetween the detector and the probe is altered if the setting isincorrect thereby enabling the setting of a cutter blade to bedetermined. The second embodiment enables the same instrument system forradial truing to be used for angle truing.

The above-mentioned objects and advantages and other objects andadvantages of the present invention will become more apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings in which:

FIG. 1 is an elevated view of a first embodiment of the inventionshowing the capacitance probe mounted on the gage slide with the probeadjacent to a cutter blade;

FIG. 2 is a plan view, partially in section, taken along lines 2-2 ofFIG. 1 and showing the assembly for securing the probe holder to thegage slide;

FIG. 3 is an elevational view'of a second embodiment of the inventionwherein a pivotally mounted contact element contacts the cutter bladeand the blade angle is inspected by measuring the gap between thecapacitance probe and the pivotal contact element;

FIG. 4 is a plan view, partially in section, taken substantially alonglines 4-4 of FIG. 3 showing the assembly for mounting the holder on agage slide;

FIG. 5 is a capacitance probe partially in section, which is used inboth embodiments of the present invention;

FIG. 6 is a schematic view of the capacitance probe circuit whichproduces an output voltage directly proportional to the average spacingbetween the end surface of the probe and the cutter blade or the contactelement; and

FIG. 7 is a schematic view illustrating the gage slide adjustments forproperly aligning the capacitance probe holders of the presentdevelopment relative to a blade in a cutter.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIGS. 1, 3 and 7, thegage units 20, are adapted to be mounted on the gage slide 22 of acutter inspection machine, of the type disclosed in the U.S. Pat No.3,099,833, to Bergemann et al. issued Aug. 6, 1963 (the disclosure ofsaid patent being incorporated herein by reference) or otherconventional cutter inspection machines. Gage unit 20 comprises a holder24 which carries a capacitance probe 26, while gage unit 20 comprises aholder 24' which carries both a capacitance probe 26' and a contactelement 28.

As schematically shown in FIG. 7, the gage slide 22 of the cutterinspection machine can be adjusted along axes 32 and 34 and angularlyadjusted about axis to position holder 24 or 24' relative to a cutter36. In the schematic representation of FIG. 7, the gage slide has beenpositioned to check the radial trueness ofa blade in cutter 36. Theslide has been adjusted about axis 30 so that the longitudinal centerline of the capacitance probe intersects the vertical axis of rotationof the cutter 36 and the end face of the probe is parallel to thecutting edge of a blade being checked. In addition, lateral and verticaladjustments have been made along axes 32 and 34, respectively, to obtainthe proper relative radial and vertical positions of the probe andcutter blade surface.

The particular mechanisms for accomplishing the movements of the gageslide are not shown in detail, since they are well known in the art.However, it is contemplated that the mechanisms for accomplishing thesemovements can be identical or similar to the mechanisms disclosed in theabovementioned Bergemann et al., patent.

The cutter 36 is rotatabiy mounted in an indexing mechanism wherein thecutter can be indexed automatically or manually rotated about its axisof rotation. It is contemplated that indexing mechanisms such as thosedisclosed by the above-mentioned Bergemann et al., patent or the patentto Hediger, U.S. Pat. No. 3,166,955, issued Jan. 26, 1965 (thedisclosure of said Hediger patent being incorporated herein byreference) can be utilized for mounting and rotating the cutter spindleduring the cutter inspection and truing operation.

Referring now to FIGS. 1 and 2, the uppermost portion 38 of capacitanceprobe holder 24 has a slot 40 for receiving an extension 42 of the gageslide 22. The width of slot 40 is sub stantially equal to, but somewhatgreater than the external diameter of extension 42 whereby the extension42 of gage slide 22 is slidably received within slot 40, while a lowerperipheral flange on the extension engages the underside of the holderto retain the holder on the extension. The innermost end of slot 40 isrounded having a curvature substantially equal to but somewhat greaterthan the external diameter of extension 42 and cooperates with aspring-biased retaining element 44 to prevent lateral movement of thecapacitance probe holder relative to the extension 42 once the extensionhas been snapped past the retaining element.

Retaining element 44 is an elongated element having a conical end 46 forengaging extension 42, a cylindrical intermediate portion 48 and anenlarged hollow, spring-retaining portion 50. Element 44 is mountedwithin an aperture 52 passing from slot 40 through portion 38 andextending perpendicular to the longitudinal centerline of slot 40.Aperture 52 is of varying internal diameter having a first portion witha diameter substantially equal to but greater than the external diameterof portion 48 of element 44 and a second portion with an internaldiameter substantially equal to but greater than the external diameterof spring-retaining portion 50 of element 44 whereby element 44 isslidably retained within aperture 52.

A hollow plug 54, which is closed at its outer end, is received withinaperture 52 and is held within the aperture by a set screw 56 orequivalent fastening means. Coil spring 48 extends between the interiorend walls of spring-retaining portion 50 of element 44 and plug 54thereby biasing element 44 toward slot 40. The inward movement of theelement 44 is limited by shoulder 60 of aperture 52 which cooperateswith shoulder 62 on element 44 and the outward movement of element 44 islimited by the opposing annular surfaces of plug 54 and element 44.However, normally there is no contact between plug 54 and element 44since the space between the annular surfaces on element 44 and plug 54is such that element 44 can be forced into aperture 52 to permit thepassage of extension 42 without the opposing ends of element 44 and plug54 contacting.

As can be seen in FIG. 2, aperture 52 is located along the sidewall ofslot 40 so that the conical surface 46 of element 44 will contact theexterior surface of extension 42 thereby firmly clamping the work holderto the extension 42. To properly align holder 24 on the slide 22, anaperture 64 is provided in the upper surface of portion 38 which, in thepreferred form, has a centerline that passes through the center ofcurvature of the rounded end portion of slot 40 and is perpendicular tothe longitudinal centerline of slot 40. This aperture 64 is adapted toreceive an aligning element such as a spring-biased pin or ball element68 to thereby properly position the work holder about the longitudinalaxis of slide 22.

An arm 72 depends from and connects portion 38 with an annular portion74 which has an aperture with a horizontal centerline extending in thesame vertical plane as the center line passing through aperture 64 andthe center of curvature of the inner end portion of slot 40. A bushing76 is slidably received within the aperture of annular portion 74 and isheld therein by a threaded locking element 78 which passes through athreaded aperture in a sidewall of bushing 76. The innermost end ofthreaded locking element 78 extends inwardly beyond the sidewall of theaperture in portion 74 and cooperates with a soft metal collar 80extending about the midportion of bushing 76 to firmly lock the bushingin place. Probe 26 is slidably received within bushing 76 and is lockedtherein by means of setscrew 82 whereby the probe can be rigidly lockedwithin bushing 76 against any axially movement during the cutterinspection and truing operation.

Referring now to FIGS. 3 and 4, a modified form of the invention isshown for measuring blade angles. The modified form of the inventioncomprises a capacitance probe 26', a

pivotal contact element 28 and a holder 24' for mounting the unit on thegage slides of cutter inspection machines such as the cutter inspectionmachine disclosed in the patent to Bergemann et al. US. Pat. No.3,099,883, issued Aug. 6, I963 or other conventional cutter inspectionmachines.

The holder 24 is an elongated element substantially channel-shaped intransverse cross section and having an upper web 90 interconnecting apair of vertically extending flanges 92, 94 which depend from web 90. Aclamping portion 38 is provided at one end of holder 24' for mountingthe holder on gage slide 22. However, since portion 38' is identical'inconstruction to portion 38 of holder 24 and cooperates with extension 42of gage slide 22 in the same manner as portion 38 of holder 24, thestructure of portion 38 will not be described in detail to avoidrepetition. However, it is to be understood that the components ofportions 38, 38 which are indicated by corresponding unprimed and primedreference numerals are identical in construction and function.

A pair of vertically extending apertures 96 and 98 are provided inholder 24' adjacent the probe retaining end of the holder. Aperture 96extends down through web 90 and portions of flanges 94, 96, whileaperture 98 extends down through web 90 and flange 92. As best shown inFIG. 4, aperture 98 is in an offset portion of holder 24' which has aplanar upper surface 100 against which a flange of the probe retainingbushing abuts to position the probe within the holder.

A slot 102 passes through web 90 and extends from aperture 96 throughaperture 98 to the free end of holder 24'. The slot cooperates with athreaded locking element 104 that passes transversely through the slotto provide a means for reducing the effective diameter of aperture 98for the purpose of clamping a probe supporting bushing within aperture98. As best shown in FIG. 4, shoulder 106 on element 104 abuts acomplementary shoulder in an unthreaded portion of aperture 108 whichpasses through web 90, while a threaded end of the locking element isreceived within a threaded portion 110 of aperture 108. With thisarrangement, clockwise movement of the knob on element 104 causes thesides of slot 102 to be drawn toward each other thereby lessening theeffective diameter of aperture 98 and counterclockwise movement of theknob allows the sides of the slot to separate thereby enlarging theeffective diameter ofaperture 98.

in addition to aperture 98, the offset portion of holder 24 has ahorizontally extending aperture 112 therein which extends through flange92 and intersects aperture 98. The aperture 112 is provided for thepurpose of viewing the lower free end of capacitance probe 26' and thecorresponding upper surface on the offset portion ofcontact element 28.

As in the first embodiment, capacitance probe 26' is housed within abushing 76 which is provided with a setscrew for locking the probewithin the central longitudinal aperture of the bushing. Annular flange114 on the bushing contacts the upper surface of the offset portion ofholder 24' to limit the downward movement of the bushing relative to theholder and position the probe within the holder. The bushing is lockedin position by the tightening of threaded element 104 which reduces theeffective diameter of aperture 98 until the bushing is firmly heldwithin the aperture.

Contact element 28 is pivotally mounted in holder 24' and issubstantially L-shaped in configuration having a pair of arms 116, 118extending at substantially right angles with respect to each other. Arm116 has an offset terminal portion 120 with a planar upper surface thatcooperates with capacitance probe 26' during the angle truing operation.The other arm 118 which depends from arm 116 is provided with a nib 122for contacting the blade surface. With this arrangement, any error inthe blade setting being checked is picked up by nib 122 causing pivotalmovement of the contact element 28. The pivotal movement of the contactelement 28 and, con sequently, the error in the blade setting ismeasured by the change of capacitance between the offset portion of thecontact element and the probe due to the change in the width of the airgap between the probe and contact element.

As best shown in FIG. 3, contact element 28 is pivotally mounted on aflexural pivot 124 extending through a pair of axially aligned apertures126, 128 in flanges 92 and 94. The vertically extending slots 130, 132in flanges 92 and 94 pass through aligned apertures 126, 128 permittinga limited expansion of the apertures during the insertion of rod 124whereby the rod is frictionally held within the apertures.

in the preferred form of the invention, probes 26, 26 can be identical.Therefore, the following detailed description of capacitance probe 26applies also to capacitance probe 26' utilized in the second embodiment.As shown in FIG. 5, the capacitance probe has a cylindrical activeelement which forms one plate of a capacitor whose other plate is formedby the cutter blade being checked or the contact element 28. The activeelement 140 is surrounded by a concentric guard ring or sleeve 142having an internal diameter somewhat greater than the external diameterof the active element 140 to insure that the field of measurement islimited to the diameter of active element 140. An outer insulating shell144 encloses both the guard sleeve and the active element and isolatesthese from ground. in the preferred form of the invention, a capacitanceprobe having the following characteristics is utilized: probe range l0mils, maximum temperature 400 F., sensitivity lOO v./in., repeatability20 microin and resolution 10 microin. A probe meeting these requirementsis commercially available and does not form a separate part of thisinvention.

As shown in FIG. 6, probes 26, 26' and the blades of the cutter 36 orthe contact element 28 form a capacitor C p which completes a negativefeed back loop that is incorporated into the high-gain amplifier of anelectronic measuring circuit. The amplifier reference V, is supplied byan internal 50 kilocycle oscillator and the output voltage of theamplifier is directly proportional to the probe-to-blade orprobe-to-contact element distance whereby the output voltage can beutilized to indicate the width of the air gap on a properly calibratedmeter. Distance meters or instruments having the required circuit forperforming such a measurement are commercially available on the markettoday.

When it is desired to use the above measuring circuit with anoscilloscope or a recorder so that a permanent record can be kept, aconventional filter balance unit (not shown) is incorporated into thecircuit to remove the high-frequency component of the circuit output toprevent this component from interfering with the displayed or recordedinformation. A balance filter unit used in the preferred form of theinvention is capable of suppressing a 50 kilocycle carrier and itsharmonies by at least a factor of 20.

Referring now in detail to FIG. 6, which is an operational diagram of anelectronic circuit utilized to measure the distance between thecapacitance probe 26, 26' and the cutter blade or contact element, theoperation of the circuit is expressed by the following formulationwherein with large values of amplifier gain A, the voltage potentialacross resistance R, approaches zero, and the following relationshipbetween currents i and i the input voltage V,, the angular velocity orwhich equals 211' times the frequency and capacitance C, exists but V,,w, and C, are all constants therefor ipk a constant, and since LCapacitance is related to the width of the air gap between the probe andthe cutter blade or contact element by the formula Thus V K: being aconstant. or

V -k d, k, being a constant, and V, is seen to be directly proportionalto d, the width of the air gap between the probe and the cutter blade orcontact element.

OPERATION When inspecting a cutter for the radial trueness of the cutterblades in a cutter inspection machine, the cutter to be checked (whichhas preferably already been checked and corrected for blade angleaccuracy) is mounted on the spindle of the machine and the capacitanceprobe 26, which has been previously mounted in the holder 24, isattached to the exten sion 42 on the gage slide 22 of the machine. inorder to adjust capacitance probe 26 relative to the cutter 36 for theradial trueness check, a reference or master blade on the cutter, suchas blade No. l, is selected. Next, the gage slide angle is set aboutaxis 30 to the pressure angle marked on the master blade. This positionsthe probe 26 so that its centerline passes substantially through thecutter axis and makes the probe face parallel to a plane tangent to thesurface of revolution swept by the blade side cutting edge. With theprobe set up in this manner, the readings obtained as a result of theoutput V, of the amplifier are dependent on the radial setting of theblades. Once the probe 26 has been angularly adjusted about axis 30, theprobe is positioned adjacent the master blade by moving the gage slidelaterally along horizontal axis 32 and in the direction of the gageslides longitudinal axis 23 along the preset angle until the centerlineof the probe intersects the blade profile a distance down from the bladetop that is equal to approximately one-half the cutting depth of theblade. To determine the proper distance between the probe and the bladefor the final adjustment along axis 32, rotate the master blade back andforth past the probe and move the gage slide laterally along axis 32until the output voltage of the amplifier indicates that the air gapbetween the probe tip and the blade surface is 0.007 inches at theminimum air gap position. The gage slide 22 can then be locked in placeand the probe 26 is in the correct operating position relative to thecutter. The truing meter or recorder is then adjusted to read zero atits peak value as the master blade is slowly rotated past the probe andthis reading serves as the reference against which the other blades willbe compared.

To obtain a reading on the trueing meter or recorder, manually rotatethe cutter blade being checked slowly by the probe 26 in the directionopposite to the direction or rotation when cutting. Due to the contourof the cutting side face, the distance between the probe 26 and theblade cutting side face gradually decreases as the probe moves relativeto the side face toward the leading cutting edge of the blade beingchecked. This causes an increase in capacitance of capacitor C, and adecrease in the voltage output V, of the amplifier. Then, as the probetip starts to pass beyond the cutting edge, the capacitance of capacitorC peaks and then begins to decrease while the output voltage V, of theamplifier reaches a nadir and then increases. The output voltage of theamplifier is measured on a voltmeter (either a digital, a panel meter ora recording type) which is calibrated to display to high resolution (10microinches) the variations in the blade to probe distance. Thecalibrations on the voltmeter are such that when the voltage output V,reaches its nadir, the meter gives a peak reading. Thus, the peakreading is obtained when the cutting edge passes the probe and this peakreading gives the indication of the radial distance of the cutting edgefrom the center of the cutter. it may be necessary to rotate the bladeby the probe several times initially to determine the correct rotationalspeed for stable peak readings. However, once the correct rotationalspeed is determined, the need for rotating the blade by the probeseveral times is eliminated. As indicated above, the cutter should berotated in the direction opposite to that in which it normally rotateswhen cutting.

For the purpose of further illustrating the present invention, the stepsof the operation will be repeated wherein a cutter blade is to be truedto plus or minus ten-millionths of an inch.

With the probe in a position which is aligned with the cutter tointersect the blade profile a distance down from the blade top that isequal to approximately one-half the cutting depth of the blade, a peakreading is obtained for the master blade which gives a 0.007 inchreading on the voltmeter which is calibrated to give a distance reading.This reading is then used to set the truing meter or recorder to zero atthis peak. The cutter is then rotated in the proper direction to thenext blade and a reading is taken. A plus reading indicates that theblade is closer to the probe then the master blade and a minus readingindicates that the blade is farther from the probe than the masterblade. After noting the reading of the blade and the direction ofcorrection needed, the blade is rotated away from the probe and theholding screw for the blade is loosened. Next, the adjusting screw forthe blade adjustment wedge is turned in the proper direction toreposition the blade after which the screw is retorqued properly. Newreadings for the blade are taken and the above-described process iscontinued until the blade is within plus or minus ten-millionths of thezero reading. Once the desired tolerance has been obtained on eachblade, a final reading is taken on each blade and recorded.

In angle truing, as in radial truing, the cutter is mounted on thespindle, the holder 24 with the contact lever 28 and capacitance probe26 is mounted on the gage slide 22 and a reference or master blade, suchas cutter blade No. 1, is selected for adjusting the contact lever 28relative to the cutter 36. After the holder 24' has been mounted on thegage slide, the gage slide angle about axis 30 is set to the pressureangle marked on the master blade. This positions the centerline of thegage slide 22 parallel to a plane tangent to the cutting side faces ofthe blade. The cutter should be rotated so that probe contacts blade0.0l00.015 behind cutter edge. At this time the index pawl should beengaged with a slot in index plate. Then, by actuating the gage slidefor reciprocal movement along axis 34, the pressure angle of the masterblade is trammed and any necessary minute adjustments in the gage slideangle to establish a zero reading on the meter over the tramming rangeat the master blade angle is made. It should be noted that in thischeck, the capacitance probe 26 is making a direct measurement throughthe lever arrangement, but the actual pick up from the blade is on thecontacting nib of the lever element 28.

After the zero reading has been established for the master blade, thecutter is indexed and the next succeeding blade is trammed in the samemanner as the master blade and over the same range with any variationsin the blade pressure angle during the tramming along the blade beingrecorded. When variations are uncovered, corrections are made byremoving the blade and replacing the adjusting wedge with a correctivewedge which has a slightly different pressure angle. The blade is thenreplaced and another check is made. After all of the blades have beencorrected, the check is repeated to insure that the angle correctionshave achieved the desired tolerance limits and the angle truingoperation is completed.

While for the purposes of illustrating the cutter inspection apparatusand methods of inspection of the present development, the invention hasbeen shown and described in connection with cutter truing operationswhere the leading cutting edges of the cutter blades are on the outside,it is to be understood that the apparatus and methods of the presentinvention can be used with and applied to cutters having the bladecutting edges on the inside or alternately on the outside and inside.With a cutter having blade cutting edges alternately on the outside andinside, it is necessary to first true one set of blades and then repeatthe operation to true the other set. Having now described the preferredembodiments of the cutter inspection assembly and the preferred methodof operating the assembly for cutter inspection and truing, it will beapparent that various modifications and equivalents can be resorted towithout departing from either the spirit or scope of the invention.

We claim:

l. A method of inspecting a plurality of cutter blades on a cutting toolfor blade-to-blade truing purposes wherein each said blade includes aleading cutting edge and a relieved side face which tapers from saidcutting edge to the back of the blade, said method comprising:

positioning said cutter blades for movement with respect to a capacitiveprobe thereby defining an air gap therebetween having a width dependentupon the position of one of said blades with respect to said capacitiveprobe,

moving a first master one of said blades past said capacitive probe byrotating said cutting tool relative to said probe so that eachsuccessive cutter blade approaches the probe from back to front wherebythe probe first senses the rear of said relieved sideface of each cutterblade, the capacitance building up to a peak which drops off relativelyfast when the cutting edge of the blade is passed, measuring and notinga minimum indicated average reference air gap for the master bladeduring said moving step, local effects due to small surfaceirregularities on said cutter blades being minimized by always measuringan instantaneous average air gap,

moving the other of said blades past said capacitive probe from back tofront in the same manner employed for the master blade, and

measuring and noting the minimum indicated average air gaps respectivelyassociated with each of said other blades if materially different thansaid reference air gap to thereby determine any untrued blades.

2. A method as in claim 1 further comprising the steps of:

individually adjusting the positioning of the said untrued ones of saidblades relative to the cutting tool in a direction to compensate for thenoted material air gap differences, and

- moving at least the adjusted ones of said blades past said referencemeans again and noting the minimum indicated air gaps if materiallydifferent than said reference air gap thereby determining if furtheradjustment is necessary.

1. A method of inspecting a plurality of cutter blades on a cutting toolfor blade-to-blade truing purposes wherein each said blade includes aleading cutting edge and a relieved side face which tapers from saidcutting edge to the back of the blade, said method comprising:positioning said cutter blades for movement with respect to a capacitiveprobe thereby defining an air gap therebetween having a width dependentupon the position of one of said blades with respect to said capacitiveprobe, moving a first master one of said blades past said capacitiveprobe by rotating said cutting tool relative to said probe so that eachsuccessive cutter blade approaches the probe from back to front wherebythe probe first senses the rear of said relieved sideface of each cutterblade, the capacitance building up to a peak which drops off relativelyfast when the cutting edge of the blade is passed, measuring and notinga minimum indicated average reference air gap for the master bladeduring said moving step, local effects due to small surfaceirregularities on said cutter blades being minimized by always measuringan instantaneous average air gap, moving the other of said blades pastsaid capacitive probe from back to front in the same manner employed forthe master blade, and measuring and noting the minimum indicated averageair gaps respectively associated with each of said other blades ifmaterially different than said reference air gap to thereby determineany untrued blades.
 2. A method as in claim 1 further comprising thesteps of: individually adjusting the positioning of the said untruedones of said blades relative to the cutting tool in a direction tocompensate for the noted material air gap differences, and moving atleast the adjusted ones of said blades past said reference means againand noting the minimum indicated air gaps if materially different thansaid reference air gap thereby determining if further adjustment isnecessary.